Apparatus and method for making glass sheet with improved sheet stability

ABSTRACT

Apparatus and equipment for making glass sheet from a glass ribbon including scoring, bending and separation in vertical state with improved glass ribbon stability provided by edge restrainers located above the score-line that also travel with substantially the same vertical velocity with the elastic ribbon. The edge restrainers on both sides of the glass ribbon serve to limit the motion and perturbation of the ribbon during scoring, bending and separation, advantageously by tensioning the glass ribbon where needed. The invention can reduce disturbance of the glass ribbon in upstream visco-elastic and/or viscous zones due to scoring, bending and separation, therefore enhance forming process stability and product attributes such as thickness variation, stress and stress variation, and the like. The invention can be particularly advantageous for making glass sheet with large width and/or low thickness using the fusion down-draw, slot down-draw, re-draw down-draw, and other down-draw processes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/378,544 filed on Aug. 31, 2010 and entitled“APPARATUS AND METHOD FOR MAKING GLASS SHEET WITH IMPROVED SHEETSTABILITY,” the content of which is relied upon and incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates in general to glass sheet-making equipmentand method. In particular, the present invention relates to glass sheetstabilizing equipment and method during forming and processing of aglass sheet in a vertical position. The present invention is useful,e.g., in making glass sheet suitable for LCD glass substrates using adown-draw process, such as fusion down-draw or slot down-draw process.

BACKGROUND

Fusion down-draw is a leading technology developed by CorningIncorporated, Corning, N.Y., U.S.A. for making thin, precision glasssheets suitable for use as liquid crystal display (LCD) glass substratesand other opto-electronic devices. This process involves introducing astream of molten glass into a forming trough called isopipe having twoside surfaces converging at a line called root, allowing the glass meltto overflow both top surfaces of the trough of the isopipe called weirs,down along both side surfaces of the isopipe as two molten glassribbons, join and fuse at the root to form a single glass ribbon, whichis then drawn down and cooled below the root to form the glass sheetwith desired dimension. In the zone below the root, the glass ribbontravels substantially vertically downward while being drawn and cooledfrom a viscous state, to visco-elastic and eventually to substantiallyelastic. The elastic glass ribbon is then cut into individual glasssheets, subjected to further finishing such as edge rounding andpolishing, and then packaged and shipped to LCD panel makers for use asTFT or color filter substrates.

One of the advantages of the fusion down-draw process for making glasssheets is that the surface quality of the glass sheets is high becausethe quality areas thereof were only exposed to the atmosphere and neverto a solid material such as the isopipe surface or the formingequipment. This process has been used successfully for making glasssheets having a width as large as 3000 mm and a thickness of about 0.6mm.

The size of LCDs for the consumer electronics market has increasedsteadily in the past decade, and along with the image quality desired.These have fueled the demand of large-width glass substrates and posedincreasingly more stringent requirements for glass sheet quality, suchas edge warp and waviness, sheet warp, surface waviness and roughness,thickness uniformity, as well as stress. In addition, consumers havedemonstrated interest in lighter electronics, which call for thinnerglass substrates having a thickness of 500 μm, 400 μm, 300 μm or evenlower.

Making large-size and/or thin glass sheets using the fusion down-draw isno easy undertaking. Over the years, experts such as the presentinventors have gained insights into the many process parameters that canimpact the desired attributes of the glass sheets. For example, it wasdiscovered that the separation of glass sheets from the ribbon when theglass is substantially elastic can lead to undesirable motion of theglass ribbon above the separation line, which can propagate into thevisco-elastic zone, and even the viscous zone, and thereby affect theattributes of the sheet formed in those zones.

Therefore, there remains a need of an apparatus and method for makingglass sheets with desirable attributes at an acceptable yield withimproved ribbon stability. The present invention satisfies this andother needs.

SUMMARY

Several aspects of the present invention are disclosed herein. It is tobe understood that these aspects may or may not overlap with oneanother. Thus, part of one aspect may fall within the scope of anotheraspect, and vice versa.

Each aspect is illustrated by a number of embodiments, which, in turn,can include one or more specific embodiments. It is to be understoodthat the embodiments may or may not overlap with each other. Thus, partof one embodiment, or specific embodiments thereof, may or may not fallwithin the ambit of another embodiment, or specific embodiments thereof,and vice versa.

Thus, a first aspect of the present disclosure relates to a process formaking a target glass sheet, comprising the following steps:

(A) providing a precursor glass ribbon comprising an elastic portion,the elastic portion having a thickness T1, a width W1, a first majorsurface S1 having a target point TP traveling with a velocity V1parallel to the gravity vector, a second major surface S2 opposing S1,S1 comprising a first peripheral region PR1, a second peripheral regionPR2 and a first center region CR1; S2 comprising a third peripheralregion PR3, a fourth peripheral region PR4 and a second center regionCR2, where PR1 is in opposing relation to PR3, PR2 is in opposingrelation to PR4, and CR1 is in opposing relation to CR2;

(B) contacting a first edge restrainer ER1 traveling with a downwardvelocity substantially equal to V1 with at least one of PR1 and PR3 at afirst restrainer location above a horizontal line SL passing through thepoint TP;

(C) contacting a second edge restrainer ER2 traveling with a downwardvelocity substantially equal to V1 with at least one of PR2 and PR4 at asecond restrainer location above the line SL;

(D) contacting a third edge restrainer ER3 with at least one of PR1 andPR3 at a third restrainer location below the line SL;

(E) contacting a fourth edge restrainer ER4 traveling with a downwardvelocity substantially equal to V1 with at least one of PR2 and PR4 at afourth restrainer location below the line SL;

(F) applying a first tensioning force F1 perpendicular to V1 to theelastic portion by the first edge restrainer, and a second tensioningforce F2 opposite to F1 to the elastic portion by the second edgerestrainer;

(G) forming a transverse score-line along the line SL on S1 below thelocations of the first edge restrainer and the second edge restrainer;

(H) applying to the elastic portion a breaking force F3 perpendicular tothe elastic portion below the score-line and a supporting force F4 abovethe score-line in a direction opposite to that of F3, the direction ofF3 being pointing from S1 to S2, thereby breaking the elastic portionalong the score-line to obtain the target glass sheet below thescore-line; and

(I) releasing ER1 and ER2 from the elastic portion after step (H).

In certain embodiments of the first aspect of the present disclosure,the process further comprises a following step (H1) after step (H) butbefore step (I):

(H1) reducing F1 and F2 continuously to substantially zero.

In certain embodiments of the first aspect of the present disclosure,the process further comprises a step (H2) after step (H) but before step(I):

(H2) reversing the directions of F1 and F2.

In certain embodiments of the first aspect of the present disclosure,the edge restrainers ER1 and ER2 contact a substantially flat area ofPR1 and/or PR3, PR2 and/or PR4, respectively.

In certain embodiments of the first aspect of the present disclosure,the distances between the edge of the glass ribbon and the locations ofthe centers of the areas of ER1 and ER2 contacting the glass ribbon areat most 40 cm, in certain embodiments at most 30 cm, in certain otherembodiments at most 20 cm, in certain other embodiments at most 10 cm,in certain other embodiments at most 5 cm.

In certain embodiments of the first aspect of the present disclosure,the distance between the score-line SL and the locations of the centersof the areas of ER1 and ER2 contacting the glass ribbon is at most 40cm, in certain embodiments at most 30 cm, in certain other embodimentsat most 20 cm, in certain other embodiments at most 10 cm, in certainother embodiments at most 5 cm.

In certain embodiments of the first aspect of the present disclosure,prior to steps (B), (C), (D), (E) and (F), S2 above the line SL exhibitsa curvature from PR1 to PR2. In certain specific embodiments, thecurvature comprises a dome-shape when viewed from the side of S2.

In certain embodiments of the first aspect of the present disclosure,the process further comprises the following step (E1) before step (F):

(E1) applying a force F5 to the elastic zone above the line SL such thatthe curvature is not reversed during steps (F) and (G) and is maintainedafter step (I).

In certain specific embodiments of the foregoing embodiment, step (E1)is carried out during steps (F), (G) and (H).

In certain specific embodiments, F5 is applied by a method selected fromthe following:

(F5 a) maintaining a higher air pressure on the side of S2 than on theside of S1;

(F5 b) blowing a gas stream against part of CR2 of S2 such that S2 ispushed toward S1;

(F5 c) pushing S2 toward S1 by a pin in contact with CR2; and

(F5 d) a combination of at least two of (F5 a), (F5 b) and (F5 c).

In certain specific embodiments of the preceding embodiment, (F5 b) isapplied, and the contact area in CR2 of the gas stream is within 50 cmabove the score-line, in certain embodiments within 40 cm above thescore-line, in certain other embodiments within 30 cm above thescore-line, in certain other embodiments within 20 cm above thescore-line.

In certain specific embodiments of the relevant preceding embodiments,the force F5 is less than 20 newton, in certain embodiments less than 10newton, in certain embodiments less than 5 newton.

In certain embodiments of the first aspect of the present disclosure,steps (B) and (C) are carried out substantially simultaneously.

In certain embodiments of the first aspect of the present disclosure,steps (D) and (E) are carried out substantially simultaneously.

In certain embodiments of the first aspect of the present disclosure, S1comprises a centerline CL1, and ER1 and ER2 are located substantiallysymmetrically with respect to CL1 in steps (F), (G) and (H).

In certain embodiments of the first aspect of the present disclosure, S1comprises a centerline CL1, and ER3 and ER4 are located substantiallysymmetrically with respect to CL1 in steps (F), (G) and (H).

In certain embodiments of the first aspect of the present disclosure,step (F) precedes step (G).

In certain embodiments of the first aspect of the present disclosure, anosing contacts S2 in the vicinity of the score-line during step (G).

In certain specific embodiments of the preceding embodiment, the nosingis a flat nosing bar extending from PR3 to PR4 contacting S2 coveringthe score-line during step (G).

In certain specific embodiments of the relevant preceding embodiments,the nosing maintains contact with S2 during step (H).

In certain specific embodiments of the relevant preceding embodiments,the nosing is released from S2 during or after step (I).

In certain embodiments of the first aspect of the present disclosure,steps (B) and (C) precede steps (D) and (E), and step (G) precedes step(F).

In certain specific embodiments of the preceding embodiment, a nosingcontacts S2 in the vicinity of the score-line during step (G).

In certain specific embodiments of the preceding embodiment, whereinduring step (G), the nosing contacts S2 and/or S1 along the score-line,and the nosing is adjusted to conform to the curvature of S2 and/or S1without substantially deforming the curvature of S2.

In certain specific embodiments of the preceding embodiment, after step(G), during step (H), the nosing maintains contact with S2 and/or S1 andis adjusted to maintain the contact area in substantially a flat plane.

In certain specific embodiment of the preceding embodiment, after step(H), during or after step (I), the nosing is adjusted to restore thecurvature of S2 to that before step (G) before the nosing is releasedfrom S1 and/or S2.

In certain embodiments of the first aspect of the present disclosure,ER1 and ER2 are selected from suction cups, clamps and rollers.

In certain embodiments of the first aspect of the present disclosure,ER1, ER2, ER3 and ER4 contact S2 and do not contact S1 during steps (F),(G) and (H).

In certain embodiments of the first aspect of the present disclosure,ER1, ER2 and the nosing are fixed on a platform capable of reciprocalvertical motion.

In certain embodiments of the first aspect of the present disclosure,the precursor glass ribbon further comprises a visco-elastic zonetraveling with the velocity V1′ within 10 meters above the score-line,in certain embodiments within 5 meters, in other embodiments within 3meters, in other embodiments within 2 meters, in other embodimentswithin 1 meter, in other embodiments within 0.5 meters, where V1′ isparallel to V1.

In certain embodiments of the first aspect of the present disclosure,the precursor glass ribbon further comprises a viscous zone within 12meters above the score-line, in certain embodiments within 10 meters, incertain embodiments within 8 meters, in certain embodiments within 5meters, in certain embodiments within 3 meters, in certain embodimentswithin 2 meters, in certain embodiments within 1 meter.

In certain embodiments of the first aspect of the present disclosure,the ratio W1/T1 of the elastic zone is at least 1000, in certainembodiments at least 2000, in certain other embodiments at least 3000,in certain other embodiments at least 5000.

In certain embodiments of the first aspect of the present disclosure, T1of the glass ribbon in CR1 in the elastic zone is at most 1.0 mm, incertain embodiments at most 0.8 mm, in certain embodiments at most 0.7mm, in certain other embodiments at most 0.6 mm, in certain embodimentsat most 0.4 mm, in certain other embodiments at most 0.3 mm.

In certain embodiments of the first aspect of the present disclosure,step (G) comprises:

(Ga) forming the score-line by scoring S1 using a mechanical scoringwheel.

In certain embodiments of the first aspect of the present disclosure,step (G) comprises:

(Gb) forming the score-line by exposing S1 to a laser beam.

In certain embodiments of the first aspect of the present disclosure,steps (B), (C), (D), (E), (F), (G) and (H) are repeated after step (I)so that a second target glass sheet is produced.

In certain embodiments of the first aspect of the present disclosure,step (A) comprises:

(A1) providing a glass melt;

(A2) forming a continuous glass ribbon from the glass melt by adown-draw process; and

(A3) cooling the continuous glass ribbon to form the precursor glassribbon.

In certain embodiments of the preceding embodiment, in step (A2), thedown-draw process is selected from a fusion down-draw process, a slotdown-draw process and a re-draw process.

A second aspect of the present disclosure relates to an apparatus formaking a target elastic glass sheet from a continuously moving precursorglass ribbon having an elastic portion comprising a first major surfaceS1, a second major surface S2 opposing S1, S1 comprising a firstperipheral region PR1, a second peripheral region PR2, and a firstcenter region CR1, S2 comprising a third peripheral region PR3 opposingPR1, a fourth peripheral region PR4 opposing PR2, and a second centerregion CR2 opposing CR1, comprising:

(I) at least one pair of rotatable edge rollers having substantiallystationery axles relative to the earth capable of engaging PR1, PR3, PR2and PR4 to provide a substantially constant downward velocity V1parallel to the gravity vector to the elastic portion of the precursorglass ribbon;

(II) a scoring device capable of providing a substantially horizontalscore-line on the surface S1;

(III) a nosing adapted for: (a) contacting and engaging S2 to stabilizethe precursor glass ribbon; (b) traveling at a velocity substantiallyequal to V1; and (c) providing a supporting force F4 perpendicular to S1during bending of the precursor glass ribbon pointing from S2 to S1;

(IV) a first edge restrainer ER1 adapted for: (a) contacting at leastone of PR1 and PR3 above the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing a tensioning force F1 tothe elastic portion perpendicular to the velocity V1;

(V) a second edge restrainer ER2 adapted for: (a) contacting at leastone of PR2 and PR4 above the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing a tensioning force F2 tothe elastic portion perpendicular to the velocity V1 having a directionopposite to F1;

(VI) a third edge restrainer ER3 adapted for: (a) contacting at leastone of PR1 and PR3 below the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing at least part of a bendingforce F3 to the elastic portion in a direction perpendicular to S1 andopposite to F4; and

(VII) a fourth edge restrainer ER4 adapted for: (a) contacting at leastone of PR2 and PR4 below the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing at least part of thebending force F3.

In certain embodiments of the second aspect of the present disclosure,ER1, ER2 and the nosing are all mounted on a common platform adapted fortraveling at a velocity substantially equal to V1.

In certain embodiments of the second aspect of the present disclosure,the apparatus further comprises:

(VIII) a gas nozzle adapted for blowing a gas stream toward CR2 toprovide a force F5 to the precursor glass ribbon having a directionpointing from S2 to S1.

In certain embodiments of the second aspect of the present disclosure,ER1, ER2, ER3 and ER4 are selected from suction cups and clamps.

In certain embodiments of the second aspect of the present disclosure,ER1 and ER2 are adapted for contacting the same and only one of S1 andS2.

In certain embodiments of the second aspect of the present disclosure,ER1 and ER2 are adapted for contacting both S1 and S2.

In certain embodiments of the second aspect of the present disclosure,ER1, ER2, ER3 and ER4 are adapted for contacting S2 only.

In certain embodiments of the second aspect of the present disclosure,the precursor glass ribbon comprises a center line CL1 on S1, and ER1and ER2 are placed essentially symmetrically relative to CL1.

In certain embodiments of the second aspect of the present disclosure,the precursor glass ribbon comprises a center line CL1 on S1, and ER3and ER4 are placed essentially symmetrically relative to CL1.

In certain embodiments of the second aspect of the present disclosure,ER1 and ER2 are adapted for contacting the precursor glass ribbon in asynchronized manner.

In certain embodiments of the second aspect of the present disclosure,ER1, ER2, ER3 and ER4 are adapted for contacting the precursor glassribbon in a synchronized manner.

One or more embodiments and/or aspects of the present disclosure haveone or more of the following advantages. First, the present inventioncan provide significant process stability to any downward glass sheetforming process by controlling and reducing upward sheet motion causedby sheet scoring, bending and separation, including fusion down-draw,slot-draw, heating-and-redraw, rolling-followed-by-drawing, and thelike. Second, by reducing downstream sheet motion that could propagateupwards to the visco-elastic and even the viscous zones of the precursorglass ribbon, the present invention can result in glass sheets havingconsistent attributes such as stress, stress distribution, thickness andthickness variation, and the like. Third, for glass sheets having a highflexibility characterized by large sheet width or low sheet thickness orboth, one of the bottlenecks for a successful commercial sheetglass-making process is yield at the BOD due to sheet motion andcurvature instability and even bow-popping. The present invention can bean enabler for making such thin and/or wide products. Lastly, thepresent invention can be easy to implement, since the edge restrainerscan be retrofitted into an existing production line or installed on anew line at a relatively low cost.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from the description or recognizedby practicing the invention as described in the written description andclaims hereof, as well as the appended drawings.

It is to be understood that the foregoing general description and thefollowing detailed description are merely exemplary of the invention,and are intended to provide an overview or framework to understandingthe nature and character of the invention as it is claimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic drawing showing a plan view of an apparatusoperating according to an embodiment of the process of the presentinvention, when viewed from the side of surface S1.

FIG. 2 is a schematic drawing showing a plan view of the same apparatusshown in FIG. 1, when viewed from the side of surface S2.

FIG. 3 is a schematic drawing showing a side view of the same apparatusshown in FIG. 1.

FIG. 4 is a schematic drawing showing the cross-section of a glassribbon operating according to an embodiment of the process of thepresent invention, where a conformable nosing is utilized.

FIG. 5 is a schematic drawing showing the cross-section of a glassribbon operating according to an embodiment of the process of thepresent invention, where a flat nosing is utilized.

FIG. 6 is a diagram showing the impact of scoring on sheet curvature.

FIG. 7 is a diagram showing the impact of scoring on sheet curvatureover a period of time during and after scoring with and without the useof edge restrainers of the present invention.

DETAILED DESCRIPTION

Unless otherwise indicated, all numbers such as those expressing weightpercents and mole percents of ingredients, dimensions, and values forcertain physical properties used in the specification and claims are tobe understood as being modified in all instances by the term “about.” Itshould also be understood that the precise numerical values used in thespecification and claims form additional embodiments of the invention.Efforts have been made to ensure the accuracy of the numerical valuesdisclosed in the Examples. Any measured numerical value, however, caninherently contain certain errors resulting from the standard deviationfound in its respective measuring technique.

As used herein, in describing and claiming the present invention, theuse of the indefinite article “a” or “an” means “at least one,” andshould not be limited to “only one” unless explicitly indicated to thecontrary. Thus, for example, reference to “a suction cup” includesembodiments having one, two or more such suction cups, unless thecontext clearly indicates otherwise.

In a typical down-draw process for making glass sheet, a viscous glassribbon is first formed at the root of the isopipe in the case of fusiondown-draw process, at the slot in the case of slot down-draw process,and by reheating in a re-draw process. The viscous glass ribbon is thendrawn down into a thinner ribbon while being cooled down. As thetemperature decreases, the glass ribbon changes from viscous tovisco-elastic and eventually becomes substantially elastic. The viscous,visco-elastic and elastic zones below the forming apparatus where theviscous ribbon is formed and processed are collectively called bottom ofdraw (BOD) for the purpose of convenience in description in the presentapplication.

Traditionally, in the BOD area, the glass ribbon is typically guided andpulled by rollers such as edge rollers until it is separated intoindividual glass sheets by a sheet separation device. The rotationalaxes of these rollers tend to be maintained stationery relative to theforming device or the earth, which provides, in part, the force thatallows the glass ribbon to travel downward continuously, enabling acontinuous glass sheet forming process. In a typical BOD set-up, thesheet separation device can comprise the following components: (1) arobot tooling which engages with the travelling ribbon by, e.g., suctioncups, secures the ribbon and moves with it; and (2) a Travelling AnvilMachine (TAM) including a vertical moving carriage to synchronize withsheet speed. On TAM, a horizontal mechanical scoring device can be usedto form a straight score-line (flaw) across the sheet (except beadregions) held in contact with and against a piece of nosing bar tofacilitate sheet separation. The nosing bar is typically slightlynarrower than the full sheet width due to the presence of enlarged edges(typically called beads). Likewise, the score-line is typically slightlyshorter than the full sheet width due to the presence of the beads. Uponthe formation of the score-line, the robot tooling bends the sheetagainst the nosing and separates the sheet from the ribbon along thescore-line. The nosing bar moves forward during scoring and separationand retracts after separation. The robot tooling transports theseparated glass sheet to a sheet transport device such as a crate or aconveyor belt. In a stable manufacture process, this process repeats toproduce multiple glass sheets, which are further finished and then usedfor the end applications, such as the glass substrates for LCDs.Co-assigned, co-pending U.S. patent application Ser. No. 12/507,248filed on Jul. 22, 2009 and entitled “METHODS AND APPARATUS FORINITIATING SCORING,” WO08/140,677 and WO08/140,678 disclose theapparatus for separating glass sheets at the BOD, the contents of whichare incorporated herein by reference in their entirety.

The scoring, bending and separation processes at the BOD can transferundesirable energy into the glass ribbon above the score-line, impartingmotion and shape changes thereto, which may propagate upwards from theelastic zone to the visco-elastic zone, and even to the viscous zone. Inan exemplary process, it can be desirable to maintain a small, stablecurvature along the width to the elastic glass ribbon before scoring,bending and separation, so that the ribbon along the draw has higherstiffness. A particularly undesirable shape change imparted by thescoring, bending and separation is the reversal of the curvaturedirection of the glass ribbon. Disturbance of the visco-elastic zonecaused by the repeated scoring, bending and separation of the glassribbon, if not controlled, can result in undesirable sheet thickness andthickness variation, sheet stress and stress variation, warp, curvatureand other critical product attributes. Process tuning to reduce thedisturbance to an acceptable level can last a long time before qualityglass sheets can be produced reliably at an acceptable yield.

The present inventors have found that the flexibility of an elasticglass ribbon, defined as the ratio of W1/T1 herein, where W1 is thewidth in mm, and T1 is the thickness in mm, greatly impacts the processstability of a down-draw process. The larger the ribbon flexibility, themore likely the glass ribbon is subjected to process instability due toBOD scoring, bending and separation. For example, a glass ribbon havinga width of over 3000 mm is much more likely to undergo curvaturereversal at the BOD than a glass ribbon having a width of lower than2500 mm, assuming both have a thickness of 700 μm. Therefore, it is muchmore difficult to make a glass sheet having a width of over 3000 mm thana glass sheet with a 2500 mm width with the same thickness with the samedegree of warp, stress, stress variation and thickness variationrequirements. By the same token, it is much more difficult to make aglass sheet having a width of 2000 mm and a thickness of 400 μm than aglass sheet with the same width but a much higher thickness of 700 μm.Significant stabilization improvement to the glass ribbon duringseparation for large-size or thin-thickness, high-flexibility glasssheet would be highly desirable.

To illustrate the possible perturbation to the visco-elastic zone of theglass ribbon caused by the scoring process in a conventional down-drawglass forming process without utilizing the stabilizing apparatus andmethod of the present invention wherein the glass ribbon is restrainedby fixed rollers the axles of which do not travel downward along withthe glass ribbon, a mathematical simulation was conducted and the resultis shown in FIG. 6. In this figure, the horizontal axis is distance fromcenter of ribbon along a straight score-line SL from one peripheralregion to the opposite peripheral region, the vertical axis is distancefrom the ribbon surface to the nosing bar. The nosing bar is shown as605. 601 shows the position of the curved glass ribbon prior to scoring,and 603 shows the curved ribbon immediately after scoring. Thus,typically the glass ribbon exhibits a bow curvature relative to avertical plane prior to scoring. During scoring, if a flat and rigidnosing 605 is used, the curvature will be pressed down to conform to thenosing surface, thus the bow shape of the glass ribbon is forced todistort. The energy inducing the distortion of the glass ribbon cancause vibration to the glass ribbon, or shape change that can propagateupwards into the visco-elastic zone, causing permanent changes to thesheet attributes, such as thickness variation, stress, warp and wavinessand the like.

Modeling and experiments further showed that the bending-separation stepafter scoring can induce even more significant ribbon shape change andvibration that can propagate into the visco-elastic zone in aconventional down-draw forming process mentioned in the precedingparagraph. Such sheet change can frequently include the reversal of thedirection of the glass ribbon called bow-popping. Bow-popping isparticularly detrimental to glass ribbon forming process stability andproduct attributes.

The present disclosure relates to a glass ribbon stabilizing apparatusand process particularly suitable for down-draw glass sheet forming.Such down-draw sheet forming process can include, but are not limitedto: fusion down-draw, slot down-draw, redraw down-draw, rolling followedby down-draw, and the like. In various aspects and embodiments, thepresent invention achieves one or more of the following: (i) reducingenergy input to the glass ribbon; (ii) dampening the ribbon motion; and(iii) reinforcing the curvature of the glass ribbon during scoring,during bending, during separation and after separation.

Next, various aspects of the present invention will be further describedby reference to the appended drawings. It should be noted that thedrawings are for illustrating specific embodiments and aspects only, andshould not be interpreted to limit the present invention in any way.Like reference signs in the drawings have the same or similar meaning.

In the present invention, edge restrainers are used to restrain bothedges of the glass ribbon before at least one of the scoring step andthe bending and separation step, as illustrated in FIGS. 1, 2 and 3. Asmentioned supra, in the conventional forming process, stationery edgerollers were used to restrain the edges of the glass ribbon to stabilizethe ribbon positions. However, due to the fixed axles of the rollers,the distance between the score-line and the rollers increases during thescoring, bending and separation steps. As the distance between thestationery rollers and the score-line grows, so is the area therebetweenand the flexibility of the ribbon in this area. The large, growing areais relatively easily subjected to distortions mentioned above. Thepresent invention, by utilizing edge restrainers that travelsubstantially at the same downward velocity with the intended score-linecapable of active tensioning of the glass ribbon, can significantlyreduce the flexibility, and maintain a high level of rigidity, of theglass ribbon between the score-line and the edge restrainer, therebysignificantly reducing the possibility of substantial sheet shapedistortion that can propagate upwards into the visco-elastic zone.

As mentioned above, the precursor glass ribbon to be processed accordingto the present invention may be produced by a fusion down-draw processusing an isopipe as disclosed in WO03/014032, WO05/081888, and the like,the relevant contents thereof are incorporated herein by reference intheir entirety. Alternatively, the precursor ribbon may be produced byslot down-draw, wherein a stream of molten glass flows through a slot ofa vessel to form a viscous ribbon, which is cooled and drawn downward toform a rigid and elastic glass sheet. Still, it is also contemplatedthat the precursor glass ribbon may be formed by reheating a pre-formedglass sheet in a furnace to viscous and/or visco-elastic state, thendrawing down to a lower thickness and cooling to elastic state. It isfurther contemplated that the precursor glass ribbon may be formed by arolling process, such as rolling a molten glass gob or a thicker glasssheet, followed by down-drawing, thinning and cooling. Thus, inparticularly advantageous embodiments of the present invention, theprecursor glass ribbon comprises a viscous zone VZ, a visco-elastic zoneVEZ and an elastic zone EZ. However, it should be noted that in certainembodiments, the precursor glass ribbon may comprise a visco-elasticzone VEZ and an elastic zone EZ only without a viscous zone VZ such asin a redraw down-draw process, and still in other embodiments, thecontinuous precursor glass ribbon may comprise an elastic zone EZ onlywithout a visco-elastic zone VEZ or a viscous zone such as in aprecision vertical glass sheet cutting process. The elastic portion ofthe precursor glass ribbon travels downward with a velocity V1 parallelto the gravity vector. While it is possible that the elastic portion maytravel with a velocity having a non-zero component V2 perpendicular tothe gravity vector in addition to V1, it is desirable in a number ofembodiments that the total velocity vector of the elastic portion isequal to V1, thus the elastic portion travels substantially downwardonly. In these embodiments, gravity has less impact on the overallribbon shape and shape change compared to those in which V2≠0.

The elastic portion of the precursor glass ribbon has two major surfacesS1 and S2, each having two peripheral regions PR1 and PR2, PR3 and PR4,a center region CR1 and CR2, respectively. In certain embodiments, suchas in the process of making glass sheets for LCD glass substrates, it ishighly desired that the center region of at least one of S1 and S2 ofthe glass ribbon be pristine and not subjected to direct contact with asolid object unless absolutely necessary. Such area to be protected istypically called “quality area.” On the other hand, the peripheral areaclose to the edges are where stabilizing and guiding devices such asrollers and the edge restrainers of the present invention are to beapplied. In certain embodiments, e.g., where the glass ribbon is formedat the BOD area of a fusion down-draw or slot down-draw process, theopposing peripheral regions, such as PR1 and PR3, PR2 and PR4, cantogether define an edge having a enlarged thickness called “bead.” It ishighly desired that the edge restrainers are located in areas of theperipheral regions where secure contact can be established. Thus, wherethe edge restrainers are suction cups, it is highly desired that wherethe edge restrainers contact the glass surface is substantially flat.The distance from the center of the edge restrainers ER1 and ER2contacting the glass surface is desired to be within 50 cm, in certainembodiments 40 cm, in certain other embodiments within 30 cm, in certainother embodiments 20 cm, still in other embodiments within 10 cm, fromthe very outside edges of the peripheral region. The closer the edgerestrainers to the very outside edge of the peripheral region, the lesslikely the edge restrainers will come into contact with the qualityarea, thus the more likely to result in larger area of useable glass.

The score-line on the glass ribbon can be chosen at any location on theglass ribbon according to the needs of the glass-making process. Factorsdetermining the location of the score-line, hence the location where aglass sheet is separated from the continuously formed glass ribboninclude, but are not limited to: (i) the dimension of the final glasssheet to be sold and/or used; (ii) dimension of the forming device;(iii) whether a defect has been detected in a glass ribbon beforeseparation; and (iv) dimension and range of the travelling anvil machinewhich can carry the scoring assembly, ER1 and ER2; and the like. Thus,the target point TP in the major surface S1 can be chosen by one skilledin the art based on the product and process. The distance between thescore-line and the center of the locations of the edge restrainers ER1and ER2 contacting the glass ribbon can be, e.g., within 50 cm, incertain embodiments within 40 cm, in certain embodiments 30 cm, incertain embodiments within 20 cm, in certain embodiments within 10 cm,in certain other embodiments within 5 cm. The closer the edgerestrainers ER1 and ER2 to the score-line, the more likely therestraining effect can be achieved during scoring, bending andseparation.

In steps (B) and (C), ER1 and ER2 are allowed to engage thecorresponding peripheral regions. In order not to disturb or alter themotion of the glass ribbon, it is desired that ER1 and ER2 travel withsubstantially the same downward velocity V1 as the target point TP wheneach of them engages the glass ribbons. Steps (B) and (C) may be carriedout at different times, as long as at the time of initial contacting,ER1 and ER2 do not exert a tensioning, compressing or twisting force tothe glass ribbon. However, it is desired that the motion of ER1 and ER2are synchronized, i.e., steps (B) and (C) are carried out atsubstantially the same time, such that the glass ribbons are restrainedand engaged on both sides in a substantially synchronized manner. It isdesired that when steps (B) and (C) are first carried out, i.e., whenER1 and ER2 are first allowed to contact and engage the glass sheet, ER1and ER2 do not exert a lateral force, i.e., force perpendicular to thegravitational vector, so that the glass ribbon is not subjected totensioning, compressing and/or twisting. The locations of ER1 and ER2 inPR1 and PR2 can be advantageously symmetrical with respect to the centerline CL1 of S1, because such symmetry can result in more stable glassribbon when F1 and F2 are applied, and less stress to other glass ribbonstabilizing devices such as upper fixed roller pairs.

In steps (D) and (E), ER3 and ER4 are allowed to engage thecorresponding peripheral regions. Edge restrainers ER3 and ER4 contactand engage the glass ribbon at a location lower than the TP, thepredetermined score-line SL, and the locations of edge restrainers ER1and ER2. In order not to disturb or alter the motion of the glassribbon, it is desired that ER3 and ER4 travel with substantially thesame downward velocity V1 as the target point TP when each of themengages the glass ribbons. Steps (D) and (E) may be carried out atdifferent times, as long as at the time of initial contacting, ER3 andER4 do not exert a tensioning, compressing or twisting force to theglass ribbon. However, it is desired that the motion of ER3 and ER4 aresynchronized, i.e., steps (D) and (E) are carried out at substantiallythe same time, such that the glass ribbons are restrained and engaged onboth sides in a substantially synchronized manner. It is desired thatwhen steps (D) and (E) are first carried out, i.e., when ER3 and ER4 arefirst allowed to contact and engage the glass sheet, ER3 and ER4 do notexert a lateral force, i.e., force perpendicular to the gravitationalvector, so that the glass ribbon is not subjected to tensioning,compressing and/or twisting.

Steps (B), (C), (D) an (E) can be carried out in any order as long asthe initial contact and engagement of ER1, ER2, ER3 and ER4 do not causeunwanted sheet motion or exert unwanted forces to the sheet.Nonetheless, it is desired that steps (B) and (C) are carried outsubstantially simultaneously and in a synchronized manner as describedsupra, and steps (D) and (E) are carried out substantiallysimultaneously and in a synchronized manner, as described supra. Inanother desired embodiment, steps (B) and (C) are carried out prior tosteps (D) and (E). In yet another desired embodiment, steps (B), (C),(D) and (E) are carried out substantially simultaneously and in asynchronized manner.

In step (F), after the initial contacting and engaging of ER1 and ER2 insteps (B) and (C), tensioning forces F1 and F2 are applied to the glassribbon above the intended score-line SL. The application of F1 and F2 isdesirably conducted in a synchronized manner, i.e., the forces F1 and F2are substantially equal in magnitude, though in opposite directions,from the start of the imposition to the reduction and the eventualelimination. It is desired that F1 and F2 are substantially parallel tothe major surface S1, such that the application thereof does not cause atwisting moment to the glass ribbon. In addition, being tensioningforces, their directions are from the center region to the peripheralregions, resulting in a tensional force inside the glass ribbon. Thetensioning forces F1 and F2 function to achieve several effects: (a)stabilizing the glass ribbon during scoring, bending and separation; (b)changing the curvature of the glass ribbon along the width W1 thereof sothat in conforms to the requirements of the nosing bar which is to bedescribed in greater detail infra; and (c) preventing or reducing motionof the glass ribbon caused by scoring, bending and separation frompropagating too far above.

In step (G), a score-line is formed on the glass ribbon below ER1, ER2,but above ER3 and ER4. Such score-line can be generated by usingmechanical, thermal and/or optical means known to one skilled in theart. Desirably, the score-line SL is substantially perpendicular to thegravity vector.

In step (H), a target glass sheet is separated from the glass ribbonalong the score-line formed in step (G) by bending and separation.Bending is effected by a supporting force F4 above or along thescore-line SL, which may be exerted by a nosing bar, and a breakingforce F3 below the score-line SL, which may be exerted by ER3 and/orER4. The two opposite forces F3 and F4 produce a bending moment to theglass ribbon along the score-line, which, at an amount large enough anddetermined by one skilled in the art, causes the breakage and separationof the target glass sheet from the ribbon.

As mentioned summarily supra, the edge restrainers ER1, ER2, ER3 and ER4travel at substantially the same vertical velocity of the elasticportion of the glass ribbon. Above the edge restrainers, the glassribbon may be further secured and guided at the edge portions by aseries of fixed roller pairs FR1, FR2, FR3 and FR4 in the elastic zoneEZ and/or the visco-elastic zone VZ. The fixed roller pairs in practicecan be pulling rollers, edge rollers or stub rolls that are eitherdriven by motors (active) or idle (passive), or a combination of bothtypes. The axles of these rollers may be substantially parallel to thegravity vector, or have an angle relative to the gravity vector. Thefixed roller pairs thus hold the glass ribbon in place, stabilize it tosome extent and provide the desired velocity to the elastic portion ofthe glass ribbon. It is highly desired that the surfaces of the fixedrollers do not slip with respect to the glass surface during operation.Thus, it is desired that the surface speed of the rollers located in theelastic region is substantially the same as the total velocity of theelastic portion of the glass ribbon. In certain desired fusion down-drawand slot down-draw processes where the glass ribbon travels with avelocity substantially parallel to the gravity vector, it is desiredthat the fixed rollers in combination provide the downward velocity V1to the glass ribbon. In those embodiments, the combination of the fixedroller pairs and the edge restrainers together stabilize the glassribbon below the forming device.

In certain embodiments of the process of the present invention, it isdesired that after step (H) but before step (I), a step (H1) is carriedout:

(H1) reducing F1 and F2 continuously to substantially zero.

By carrying out step (H1), the glass ribbon above the score-line willremain substantially restrained by ER1 and ER2 immediately after bendingand separation of a glass sheet from the glass ribbon. It is believedthat a sudden reduction of F1 and/or F2 to substantially zero, e.g., thecomplete elimination of the tensioning force by ER1 and ER2 in a shortperiod of time, can cause the energy stored in the glass ribbon as aresult of the tensioning to uncontrollably release, which may result inthe generation of undesirable ribbon motion that can propagate upwardsto the visco-elastic zone VEZ and even the viscous zone VZ. The slow andcontrolled reduction of F1 and F2, hence the slow and controlled releaseof ER1 and ER2 from the glass ribbon above the score-line, allows forthe slow release and absorption of the energy stored in the glass ribbondue to the forced shape change during scoring, bending and separation.It is desired that after at any time when F1 and F2 are applied to theglass ribbon, the magnitude of F1 and F2 are substantially the same andthe directions thereof are substantially opposite to each other.

In certain embodiments, after step (H) but before step (I), optionallyafter the step (H1) described supra, a step (H2) is carried out:

(H2) reversing the directions of F1 and F2.

It is believed that by reversing the directions of F1 and F2, i.e., bychanging the forces applied by ER1 and ER2 from tensioning tocompressing after bending and separation and after F1 and F2 are bothreduced to substantially zero can be beneficial to maintain thedirection of the curvature (bow) of the glass ribbon. One skilled in theart can determine the right amount of compressive forces F1 and F2 instep (H2), such that the glass ribbon would not be significantly pressedto buckle along the width (W1) of the glass ribbon to an extentsignificantly larger than the original curvature thereof without theapplication of a lateral force thereto (i.e., where F1=F2=0). Similar tostep (H1), after step (H2), it is generally desired that before step(I), the forces F1 and F2 are gradually reduced to zero so that nounwanted motion of the glass ribbon may be produced as a result of thereduction and elimination of F1 and F2.

As described supra, the present invention, by utilizing edge restrainersER1 and ER2, has the capability to stabilize the glass ribbon duringscoring, bending and separation. The glass ribbon may be substantiallyflat above the score-line before the engagement of ER1, ER2, ER3, ER4and/or the nosing. In certain advantageous embodiments, the glass ribbonexhibits a curvature from PR1 and PR2 before the engagement of the edgerestrainers to the glass ribbon. Such natural curvature may be causedby, e.g., intentional forming set-up, cooling after forming andmechanical impartation as a result of the tensioning and/or compressingforces applied by the driving mechanisms such as edge pulling rolls,stub-rolls, and the like. Such curvature from PR1 to PR2, when viewedfrom the side of the surface S2, may have a shape with protruding centerregion CR2, called ‘bowl-shape” or a shape with a depressing centerregion CR1, called “dome-shape.”

As mentioned supra, during the scoring, bending and separation of atarget glass sheet from the glass ribbon, if the glass ribbon exhibits acurvature from PR1 and PR2 as discussed above prior to the engagement ofER1, ER2, ER3, ER4 and/or the nosing, it is highly undesirable that thecurvature of the glass ribbon reverses direction.

Such curvature reversal is sometimes called “bow-popping,” which cancause significant amount of sheet motion that can travel upwards intothe visco-elastic zone VEZ and/or the viscous zone VZ, which, in turn,can alter the attributes of the glass ribbon such as stress and stressdistribution, thickness variation and the like. In order to furtherstabilize the glass ribbon, in certain embodiments of the presentinvention, it is further desired that a step (E1) is carried out priorto step (F):

(E1) applying a force F5 to the elastic zone above the line SL such thatthe curvature is not reversed during steps (F) and (G) and is maintainedafter step (I).

Thus, to that end, the direction of force F5 is desired to reinforce thecurvature. Therefore, it is desired that F5 points from S1 to S2 if thecurvature exhibits a depression (dip) from PR1 to PR2 when viewed fromthe surface of S1, and vice versa. In certain embodiments, the step (E1)can be carried out during steps (F), (G) and (H), i.e., during thetensioning, scoring, bending and separation of the glass ribbon. ForceF5 can be applied according to one of the following approaches, e.g.:

(F5 a) maintaining a higher air pressure on the side of S2 than on theside of S1;

(F5 b) blowing a gas stream against part of CR2 of S2 such that S2 ispushed toward S1;

(F5 c) pushing S2 toward S1 by a pin in contact with CR2; and

(F5 d) a combination of at least two of (F5 a), (F5 b) and (F5 c).

If approach (F5 b) is chosen to effect force F5, in certain embodiments,the contact area in CR2 of the gas stream can be chosen to be within 50cm above the score-line, in certain embodiments within 40 cm above thescore-line, in certain other embodiments within 30 cm above thescore-line, in certain other embodiments within 20 cm above thescore-line. In general, a short distance between the primary area towhich F5 is applied and the score-line allows for a small amount of F5to achieve the shape-preserving effect. Thus, in these embodiments,force F5 can be less than 20 newton, in certain embodiments less than 10newton, in certain embodiments less than 5 newton.

In certain embodiments of the process of the present invention, step (G)precedes step (F), i.e., edge restrainers ER1 and ER2 do not apply atensioning force to the peripheral regions of the glass ribbon duringthe scoring step. Such embodiments can be advantageously adopted wherethe glass ribbon has a relatively small width, such as a width ofsmaller than 2000 mm where the glass ribbon in general exhibits arelatively high stiffness, or where the glass ribbon before steps (B),(C), (D) and (E) is substantially planar and does not exhibit acurvature from one side to the other. However, in certain embodiments,it is highly advantageous that step (F) is carried out prior to step(G), such that the glass ribbon is stabilized by the tension forces F1and F2 above the score-line during the step of scoring. It should benoted that, even though the edge restrainers ER1 and ER2 provide someedge restraining function without tensioning forces F1 and F2intentionally applied, the application of F1 and F2 can function tofurther stiffen the glass ribbon, and to conform the glass ribbon to thenosing bar NB which can be flat.

During step (G), a nosing bar NB may be used to support the area in thevicinity of the score-line SL on surface S2 so that a mechanicalscore-wheel can press surface S1 along the score-line SL, scribe thesurface S1 to form a continuous scratch SL extending from PR1 to PR2. Asmentioned supra, it is desired in certain embodiments that SL issubstantially horizontal and perpendicular to the gravity vector, eventhough a slant score-line having a non-zero angle to the gravity vectormay be also acceptable in other embodiments. The nosing bar NB supportsthe glass ribbon and prevents the glass ribbon from moving when amechanical wheel presses down on surface S1. Detailed description ofnosing bar material, shape, location, and operation, and the score-wheellocation, material and operation can be found in, e.g., WO08/140,677 andWO08/140,678.

Thus, in certain embodiments, the nosing bar NB comprises asubstantially flat piece of material extending from PR3 and PR4contacting S2. When viewed from S1 in a direction perpendicular to S1,the score-line SL thus may fall within or slightly above or below thenosing bar NB area. Because the glass ribbon separates the nosing bar NBand the score-line SL, the nosing bar area is considered to be in thevicinity of the score-line SL in all three scenarios. It is believedthat where the nosing bar NB area covers the score-line SL, the glassribbon is more stable due to the direct support provided.

In certain embodiments, during step (H), when the glass ribbon is bentand separated, the nosing bar remains in direct contact with surface S2of the glass ribbon. In these embodiments, the nosing bar NB provides atleast part of the support force F4, which, in combination with F3,generates the bending moment required for the glass ribbon to bend andseparate.

After the separation of the glass sheet from the glass ribbon at the endof step (H), the edge restrainers ER1 and ER2 are released from theglass ribbon in step (I). Where a nosing bar NB contacts S2 in step (H),it is desired that the nosing bar NB is released from S2 during or afterstep (I).

As mentioned supra and illustrated in FIG. 5, in certain embodiments,the nosing bar NB contacting surfaces S2 can be flat. In theseembodiments, it is desired that prior to step (G) where the surface S1is scored, step (F) is carried out such that the glass ribbon isflattened by the tensioning forces F1 and F2 to conform to the flatnosing bar. In certain other embodiments, it is highly advantageous touse a curved nosing bar NB shown in FIG. 4 that can be adjusted toconform to the curvature of S2 and/or S1 without substantially alteringthe curvature of S2. The conformable nosing may be configured to contactonly S2, or both S1 and S2. Details of such conformable nosing includingmaterial choice, structures and operation are provided in WO08/140,677and WO08/140,678, the contents of both of which are incorporated hereinby reference in their entirety. In such embodiments utilizing aconformable nosing, it is highly advantageous that step (F) is notcarried out prior to step (G), such that the tensioning forces F1 and F2are not applied to alter the surface curvature of the glass ribbon. Inthese embodiments, step (F) is advantageously carried out after step (G)but prior to step (H), such that during bending and separation, theglass ribbon is further stabilized and tensioned by the edge restrainersER1 and ER2. Further, it is advantageous in certain embodiments toadjust the nosing curvature in step (H) such that the nosing issubstantially flat to facilitate the bending and separation of the glassribbon. Still further, in those embodiments, it is advantageous toadjust the nosing curvature after step (H) but before step (I) toconform to the curvature of S2 before step (G) is carried out so thatwhen ER1 and ER2 is released from the glass ribbon, the curvature of theglass ribbon can restore to its natural shape when no externaltensioning or compressing by the edge restrainers and the nosing barexists.

The edge restrainers of the present invention can take various forms.For example, each of ER1 and ER2 can be a suction cup, a clamp or a pairof rollers. The materials directly contacting surface S1 and/or S2,either of a suction cup or a clamp or roller pairs, can beadvantageously made of high-temperature polymer materials, such assilicone rubbers, polytetrafluoroethylene, and the like. The edgerestrainers establish an intimate contact with the peripheral regions ofS1 and/or S2, can travel downward with a velocity substantially equal toV1, and can exert tensioning and/or compressing forces in desired amountto the glass ribbons via the surface contact. One skilled in the art ofglass sheet handling can design and choose the proper material, size,structure, and actuating devices of the suction cups, clamps and edgerollers according to the size, velocity, thickness, temperature, andother parameters of the glass ribbon being handled.

In certain embodiments, the edge restrainers ER1 and ER2 contact only S1and do not contact S2 during steps (F), (G) and (H). In certainembodiments, the edge restrainers ER1 and ER2 contact only S2 and do notcontact S1 during steps (F), (G) and (H). In other embodiments, the edgerestrainers ER1 and ER2 contact both S1 and S2 during steps (F), (G) and(H). In certain embodiments, the edge restrainers ER3 and ER4 contactonly S1 and do not contact S2 during steps (F), (G) and (H). In otherembodiments, the edge restrainers ER3 and ER4 contact only S2 and do notcontact S1 during steps (F), (G) and (H). In other embodiments, the edgerestrainers ER3 and ER4 contact both S1 and S2 during steps (F), (G) and(H). Where clamps are used as the edge restrainers, they typicallycontact both S1 and S2 to provide the needed restraining, tensioning andcompressing functions. Where suction cups are used as the edgerestrainers, choices can be made to contact either or both sides of S1and S2.

As is clear from the description supra, while only one edge restrainerER1 and ER2 is shown in each peripheral region PR1 and PR2 of the glassribbon in FIGS. 1, 2 and 3, multiple edge restrainers ER1 and ER2 may beused to contact the ribbon surface S1 and/or S2 simultaneously orsequentially. For example, in each peripheral region PR1 or PR2, 2, 3 oreven more edge restrainers ER1 and ER2 may be used to collectivelyprovide the edge restraining, guiding and tensioning functions. Themultiple edge restrainers ER1 contacting PR1 may be termed ER1(1),ER1(2), . . . , ER1(n), and the multiple edge restrainers ER2 contactingPR2 may be termed ER2(1), ER2(2), . . . , ER2(n), and the like. Thelocations of ER1(1), ER1(2), . . . , ER1(n) may form a horizontal orvertical line, a triangle pattern, a square pattern, a circular pattern,and the like. Similarly, the locations of ER2(1), ER2(2), . . . , ER2(n)may form a horizontal or vertical line, a triangle pattern, a squarepattern, a circular pattern, and the like. Nonetheless, it is desired incertain embodiments that the pattern formed by the locations of ER1(1),ER1(2), . . . , ER1(n) and the pattern formed by the locations ofER2(1), ER2(2), . . . , ER2(n) are symmetrical with respect to thecenterline CL1 of S1. Further, the operation of the ER1(1), ER1(2), . .. , ER1(n) and ER2(1), ER2(2), . . . , ER2(n) are advantageouslysynchronized and symmetrical with respect to the centerline CL1. Withthe use of a common platform such as a traveling anvil machine, suchsynchronization and symmetry can be relatively easy to achieve.

Similarly, as is clear from the description supra, while only one edgerestrainer ER3 and ER4 is shown in each peripheral region PR1 and PR2 ofthe glass ribbon in FIGS. 1, 2 and 3, multiple edge restrainers ER3 andER4 may be used to contact the ribbon surface S1 and/or S2simultaneously or sequentially. For example, in each peripheral regionPR1 or PR2, 2, 3 or even more edge restrainers ER3 and ER4 may be usedto collectively provide the edge restraining, guiding and tensioningfunctions. The multiple edge restrainers ER3 and ER4 contacting PR1 maybe termed ER3(1), ER3(2), . . . , ER3(n), and the multiple edgerestrainers ER4 contacting PR2 may be termed ER4(1), ER4(2), . . . ,ER4(n), and the like. The locations of ER3(1), ER3(2), . . . , ER3(n)may form a horizontal or vertical line, a triangle pattern, a squarepattern, a circular pattern, and the like. Similarly, the locations ofER4(1), ER4(2), . . . , ER4(n) may form a horizontal or vertical line, atriangle pattern, a square pattern, a circular pattern, and the like.Nonetheless, it is desired in certain embodiments that the patternformed by the locations of ER3(1), ER3(2), . . . , ER3(n) and thepattern formed by the locations of ER4(1), ER4(2), . . . , ER4(n) aresymmetrical with respect to the centerline CL1 of 51. Further, theoperation of the ER3(1), ER3(2), . . . , ER3(n) and ER4(1), ER4(2), . .. , ER4(n) are advantageously synchronized and symmetrical with respectto the centerline CL1. With the use of a common platform such as a robottooling, such synchronization and symmetry can be relatively easy toachieve.

In certain embodiments, in order to synchronize the operation of theedge restrainers ER1 and ER2, they may be installed on a unitaryplatform extending from one peripheral region to the other of the glassribbon capable of traveling at a velocity substantially equal to V1 ofthe glass ribbon during operation. In certain embodiments, the platformis advantageously capable of reciprocal vertical motions such that steps(B)-(I) can be repeated in multiple restraining, scoring, bending andseparation operations. Furthermore, in certain embodiments, it isdesired that the edge restrainers ER1, ER2, the nosing bar, and thescoring assembly are all installed on a unitary platform capable ofreciprocal vertical motions allowing repeated operations. Such platformis sometimes called traveling anvil machine (TAM) because it providesthe anvil function during scoring, bending and separation steps.Detailed description of a TAM is provided in, e.g., U.S. Pat. Nos.6,616,025 and WO08/133,800, the contents of both of which areincorporated herein by reference in their entirety.

The edge restrainers ER3 and ER4 are advantageously part of the robottooling for handling glass sheets at the BOD area of a verticaldown-draw process. ER3 and ER4 can provide the required breaking forceF3, in combination or solely, that bends and breaks the glass ribbonalong the score-line. At the end of step (H) and in step (I), ER3 andER4 may carry the separated glass sheets to a downstream location ormechanism, such as a crate, a conveyer belt, a transporting platform,and the like. Description of a robot tooling is provided in, e.g., U.S.Pat. No. 6,616,025, the content of which is incorporated herein byreference in its entirety.

As mentioned supra, the process of the present invention is particularlyadvantageous for a glass-making process, such as a fusion down-draw,slot-draw or re-draw process, where the precursor glass ribboncomprises, in addition to the elastic zone which is to be scored, bentand separated, a visco-elastic zone directly connected with the elasticzone that can be negatively affected by motion in the elastic zone. Thevisco-elastic zone may travel at a vertical velocity V1′ that issubstantially equal to V1 or slightly lower than V1 due to possiblethinning in this zone. In certain embodiments, the visco-elastic zone iswithin 10 meters above the score-line, in certain embodiments within 5meters, in other embodiments within 3 meters, in other embodimentswithin 2 meters, in other embodiments within 1 meter, in otherembodiments within 0.5 meter.

As mentioned supra, the process of the present invention is particularlyadvantageous for a glass-making process, such as a fusion down-draw,slot-draw or re-draw process, where the precursor glass ribboncomprises, in addition to the elastic zone which is to be scored, bentand separated, a visco-elastic zone directly connected with and abovethe elastic zone, as well as a viscous zone directly connected with andabove the visco-elastic zone, that can be negatively affected by motionin the elastic zone. In certain embodiments, the viscous zone is within12 meters above the score-line, in certain embodiments within 10 meters,in certain embodiments within 8 meters, in certain embodiments within 5meters, in other embodiments within 3 meters.

As discussed supra, the process of the present invention is particularlyadvantageous for a process for making a glass sheet having a precursorribbon having a high flexibility (low stiffness) defined by the ratioW1/T1. In particular, the process of the present invention isparticularly advantageous for making a glass sheet having a W1/T1 ratioof at least 1000, in certain embodiments at least 2000, in certain otherembodiments at least 3000, in certain other embodiments at least 5000,in certain other embodiments at least 6000, in certain other embodimentsat least 7000, in certain other embodiments at least 8000, in certainother embodiments at least 9000, in certain other embodiments at least10000. The edge restrainers ER1 and ER2, simple as they appear, providesignificant stability improvement to the manufacture process and productattribute consistency, especially thickness variation, stress and stressdistribution for glass sheets having a high W1/T1 ratio.

In particular, the present invention process is particularlyadvantageous for making glass sheets having a thickness T1 of at most1.0 mm, in certain embodiments at most 0.8 mm, in certain embodiments atmost 0.7 mm, in certain other embodiments at most 0.6 mm, in certainembodiments at most 0.4 mm, in certain other embodiments at most 0.3 mm.

In step (G), the score-line on surface S1 may be formed by mechanicalscoring using a mechanical scoring wheel detailed in WO08/133,800, thecontent of which is incorporated herein by reference in its entirety.Alternatively, laser scoring described in, e.g., WO08/140,818,WO09/045,319, WO09/067,164, and WO09/091,510, the contents of which areincorporated herein by reference in its entirety, may be used to makethe score-line as well. The combination of laser scoring and the use ofedge restrainer would be especially advantageous for making glass sheetshaving low stiffness, such as those having a large width and/or a lowthickness described above.

As mentioned above, in a continuous glass manufacture process, theprecursor glass ribbon provided in step (A) is usually continuous, andthe glass ribbon needs to be scored and separated repeatedly to makemultiple glass sheet products. In such a continuous glass sheet makingprocess such as one using the fusion down-draw glass forming technology,steps (B), (C), (D), (E), (F), (G), (H) and (I) can be repeated,especially where a TAM having reciprocal vertical motion capability isused, so that multiple glass sheets can be made continuously withconsistent quality and significant process stability. Robot tooling canbe programmed to repeatedly engage the edge restrainers ER3, ER4 withthe glass ribbon surface, bending the glass ribbon, transport theseparated glass sheet to a downstream device, release the glass sheetfrom the edge restrainers ER3 and ER4, and then return to thepredetermined position to engage the glass ribbon to be separated in thenext cycle.

Thus, examples of step (A) can comprise the following steps:

(A1) providing a glass melt;

(A2) forming a continuous glass ribbon from the glass melt by a fusiondown-draw or slot down-draw process; and

(A3) cooling the continuous glass ribbon to form the precursor glassribbon.

The fusion down-draw process is described in detail, e.g., inWO03/014032, WO05/081888, the contents of which are incorporated hereinby reference in their entirety.

A second aspect of the present invention is an apparatus for making atarget elastic glass sheet from a continuously moving precursor glassribbon comprising an elastic portion having a first major surface S1, asecond major surface S2 opposing S1, S1 comprising a first peripheralregion PR1, a second peripheral region PR2, and a first center regionCR1, S2 comprising a third peripheral region PR3 opposing PR1, a fourthperipheral region PR4 opposing PR2, and a second center region CR2opposing CR1, comprising:

(I) at least one pair of rotatable edge rollers having substantiallystationery axles relative to the earth capable of engaging PR1, PR3, PR2and PR4 to provide a substantially constant downward velocity V1parallel to the gravity vector to the precursor glass ribbon;

(II) a scoring device capable of providing a substantially horizontalscore-line on the surface S1;

(III) a nosing adapted for: (a) contacting and engaging S2 to stabilizethe precursor glass ribbon; (b) traveling at a velocity substantiallyequal to V1; and (c) providing a supporting force F4 perpendicular to S1during bending of the precursor glass ribbon pointing from S2 to S1;

(IV) a first edge restrainer ER1 adapted for: (a) contacting at leastone of PR1 and PR3 above the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing a tensioning force F1 tothe elastic portion perpendicular to the velocity V1;

(V) a second edge restrainer ER2 adapted for: (a) contacting at leastone of PR2 and PR4 above the score-line; (b) traveling at a velocitysubstantially equal to V1;

and (c) providing a tensioning force F2 to the elastic portionperpendicular to the velocity V1 having a direction opposite to F1;

(VI) a third edge restrainer ER3 adapted for: (a) contacting at leastone of PR1 and PR3 below the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing at least part of a bendingforce F3 to the elastic portion in a direction perpendicular to S1 andopposite to F4; and

(VII) a fourth edge restrainer ER4 adapted for: (a) contacting at leastone of PR2 and PR4 below the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing at least part of thebending force F3.

Various components of the apparatus of the present invention has beendescribed supra. For example, in certain particularly advantageousembodiments, ER1, ER2 and the nosing are all mounted on a singleplatform (such as a traveling anvil machine) adapted for traveling at avelocity substantially equal to V1. Likewise, in certain particularlyadvantageous embodiments, ER3 and ER4 are mounted on a robot tooling, asdescribed supra.

In certain embodiments of the apparatus of the present invention, Theapparatus further comprises:

(VIII) a gas nozzle adapted for blowing a gas stream toward CR2 toprovide a force F5 to the precursor glass ribbon having a directionpointing from S1 to S2.

The temperature and flow rate of the gas provided by the nozzle can bedetermined according to the needs of specific sheet-making process basedon factors such as sheet width, sheet thickness, sheet materialcomposition, sheet surface curvature, and the like.

In certain embodiments of the apparatus of the present invention, ER1,ER2, ER3 and ER4 are either suction cups or clamps. In certainembodiments, ER1, ER2, ER3 and ER4 comprise actuators, valves and othercontrol mechanisms that can be used to adjust the location, vacuumexerted, clamping force, tensioning force, compressing force, engaging,disengaging, and the like, of the suction cups and/or clamps as needed.

In certain embodiments, it is recommended that edge restrainers ER1 andER2 are 70 mm to 150 mm measured from the score-line. Lab test datasuggests wider range could be used, e.g., 50 mm to 200 mm. Equipmentspace constraints can be another determining factor. In certainembodiments, to save space, suction cups ER1 and ER2 are horizontallyaligned with robot tooling suction cups ER3 and ER4. They need to beable to accommodate sheet walk as robot tooling. Cup arrangement can bevertical, horizontal or triangular with 2 to 3 on each side ofrestrainer unit to deliver sufficient load carrying capacity (noslippage and long suction cup life). Suction cups can engage the ribbonfrom either 51 and/or S2 sides. In certain embodiments, it is highlydesired that ER3 and ER4 at least engage 51, as during step (H), whenthe glass ribbon is bent and separated, the ribbon will push instead ofpull ER3 and ER4, resulting in a more stable process. Tensioning forcesF1 and F2 can range from 0 to 50 pound (0 to 222 newton) in certainembodiments, depending from factors such as sheet size, sheet thicknessand the like. In certain advantageous embodiments, the edge restrainersER1 and ER2 have all the position alignment capabilities as currentrobot tooling. If plastic materials are used to make ER1 and ER2, ER1and ER2 may be thermally shielded from hotter upstream components. Incertain embodiments, ER1 and ER2 are placed on articulating arms, suchthat during certain events, such as upstream catastrophic sheetbreakage, ER1 and ER2 can be moved away from the path of the fallingglass pieces.

FIG. 7 shows the impact on ribbon motion reduction and glass ribboncurvature reinforcement by using the edge restrainers according to oneembodiment of the present invention based on dynamic process simulation.In this figure, the horizontal axis is time in second, the vertical axisshows the distance between a glass surface in the vicinity of thescore-line and a sensor having a fixed position, 700 stands for a flatnosing bar, the range 701 represents the scoring period, the range 703represents a period after scoring when the score wheel does not contactthe glass surface, the solid-line curve 705 represents an embodimentwhere the glass ribbon is not restrained by edge restrainers accordingto the present invention, and the dotted-line curve 707 represents anembodiment where the glass ribbon is restrained by edge restrainersaccording to the present invention. In the embodiment where edgerestrainers according to the present invention are used, ribbon motionis significantly reduced and bow shape reinforced (fewer propensitiesfor bow pop).

It will be apparent to those skilled in the art that variousmodifications and alterations can be made to the present inventionwithout departing from the scope and spirit of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A process for making a target glass sheet,comprising the following steps: (A) providing a precursor glass ribboncomprising an elastic portion, the elastic portion having a thicknessT1, a width W1, a first major surface S1 having a target point TPtraveling with a velocity V1 parallel to the gravity vector, a secondmajor surface S2 opposing S1, S1 comprising a first peripheral regionPR1, a second peripheral region PR2 and a first center region CR1; S2comprising a third peripheral region PR3, a fourth peripheral region PR4and a second center region CR2, where PR1 is in opposing relation toPR3, PR2 is in opposing relation to PR4, and CR1 is in opposing relationto CR2; (B) contacting a first edge restrainer ER1 traveling with adownward velocity substantially equal to V1 with at least one of PR1 andPR3 at a first restrainer location above a horizontal line SL passingthrough the point TP; (C) contacting a second edge restrainer ER2traveling with a downward velocity substantially equal to V1 with atleast one of PR2 and PR4 at a second restrainer location above the lineSL; (D) contacting a third edge restrainer ER3 with at least one of PR1and PR3 at a third restrainer location below the line SL; (E) contactinga fourth edge restrainer ER4 traveling with a downward velocitysubstantially equal to V1 with at least one of PR2 and PR4 at a fourthrestrainer location below the line SL; (F) applying a first tensioningforce F1 perpendicular to V1 to the elastic portion by the first edgerestrainer, and a second tensioning force F2 opposite to F1 to theelastic portion by the second edge restrainer; (G) forming a transversescore-line along the line SL on S1 below the locations of the first edgerestrainer and the second edge restrainer; (H) applying to the elasticportion a breaking force F3 perpendicular to the elastic portion belowthe score-line and a supporting force F4 above the score-line in adirection opposite to that of F3, the direction of F3 being pointingfrom S1 to S2, thereby breaking the elastic portion along the score-lineto obtain the target glass sheet below the score-line; and (I) releasingER1 and ER2 from the elastic portion after step (H).
 2. A process inaccordance with claim 1, further comprising a step (H1) after step (H)but before step (I): (H1) reducing F1 and F2 continuously tosubstantially zero.
 3. A process in accordance with claim 1, whereinprior to steps (B), (C), (D), (E) and (F), S2 above the line SL exhibitsa curvature from PR1 to PR2.
 4. A process in accordance with claim 3,further comprising the following step (E1) before step (F): (E1)applying a force F5 to the elastic zone above the line SL such that thecurvature is not reversed during steps (F) and (G) and is maintainedafter step (I).
 5. A process in accordance with claim 1, wherein steps(F) precedes step (G).
 6. A process in accordance with claim 5, whereina nosing contacts S2 in the vicinity of the score-line during step (G).7. A process in accordance with claim 6, wherein the nosing maintainscontact with S2 during step (H).
 8. A process in accordance with claim6, wherein during step (G), the nosing contacts S2 in the vicinity ofthe score-line, and the nosing is adjusted to conform to the curvatureof S2 without substantially deforming the curvature of S2.
 9. A processin accordance with claim 1, wherein ER1 and ER2 are selected fromsuction cups, clamps and rollers.
 10. A process in accordance with claim1, wherein ER1, ER2, ER3 and ER4 contact S2 and do not contact S1 duringsteps (F), (G) and (H).
 11. A process in accordance with claim 6,wherein ER1, ER2 and the nosing are fixed on a platform capable ofreciprocal vertical motion.
 12. A process in accordance with claim 1,wherein the precursor glass ribbon further comprises a visco-elasticzone traveling with a velocity V1′ within 10 meters above thescore-line, where V1′ is parallel to V1.
 13. A process in accordancewith claim 1, wherein the precursor glass ribbon further comprises aviscous zone within 12 meters of the score-line.
 14. A process inaccordance with claim 1, wherein the ratio W1/T1 of the elastic zone isat least
 1000. 15. An apparatus for making a target elastic glass sheetfrom a continuously moving precursor glass ribbon comprising an elasticportion having a first major surface S1, a second major surface S2opposing S1, S1 comprising a first peripheral region PR1, a secondperipheral region PR2, and a first center region CR1, S2 comprising athird peripheral region PR3 opposing PR1, a fourth peripheral region PR4opposing PR2, and a second center region CR2 opposing CR1, comprising:(I) at least one pair of rotatable edge rollers having substantiallystationery axles relative to the earth capable of engaging PR1, PR3, PR2and PR4 to provide a downward velocity V1 parallel to the gravity vectorto the precursor glass ribbon; (II) a scoring device capable ofproviding a substantially horizontal score-line on the surface S1; (III)a nosing adapted for: (a) contacting and engaging S2 to stabilize theprecursor glass ribbon; (b) traveling at a velocity substantially equalto V1; and (c) providing a supporting force F4 perpendicular to S1during bending of the precursor glass ribbon pointing from S2 to S1;(IV) a first edge restrainer ER1 adapted for: (a) contacting at leastone of PR1 and PR3 above the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing a tensioning force F1 tothe elastic portion perpendicular to the velocity V1; (V) a second edgerestrainer ER2 adapted for: (a) contacting at least one of PR2 and PR4above the score-line; (b) traveling at a velocity substantially equal toV1; and (c) providing a tensioning force F2 to the elastic portionperpendicular to the velocity V1 having a direction opposite to F1; (VI)a third edge restrainer ER3 adapted for: (a) contacting at least one ofPR1 and PR3 below the score-line; (b) traveling at a velocitysubstantially equal to V1; and (c) providing at least part of a bendingforce F3 to the elastic portion perpendicular to S1 in a directionopposite to F4; and (VII) a fourth edge restrainer ER4 adapted for: (a)contacting at least one of PR2 and PR4 below the score-line; (b)traveling at a velocity substantially equal to V1; and (c) providing atleast part of the bending force F3.
 16. An apparatus according to claim15, wherein ER1, ER2 and the nosing are all mounted on a common platformfor traveling at a velocity substantially equal to V1.
 17. An apparatusaccording to claim 15, wherein ER1, ER2, ER3 and ER4 are either suctioncups or clamps.
 18. An apparatus according to claim 15, wherein ER1,ER2, ER3 and ER4 contact S2 only.
 19. An apparatus according to claim15, wherein ER1 and ER2 are adapted for contacting the precursor glassribbon in a synchronized manner.
 20. An apparatus according to claim 15,wherein ER1, ER2, ER3 and ER4 are adapted for contacting the precursorglass ribbon in a synchronized manner.